When user explicitly configures an agent model in oh-my-opencode.json,
that model should take priority over the active model in OpenCode's config
(which may just be the system default, not a deliberate UI selection).
This fixes the issue where user-configured models from plugin providers
(e.g., google/antigravity-*) were being overridden by the fallback chain
because config.model was being passed as uiSelectedModel regardless of
whether the user had an explicit config.
The fix:
- Only pass uiSelectedModel when there's no explicit userModel config
- If user has configured a model, let resolveModelPipeline use it directly
Fixes#1573
dbf584af95